This invention relates to the art of testing networks, such as printed circuit boards, to verify that network nodes of the network are interconnected in accordance with the design of the network.
Manual continuity-testing of a network, whether it be a wiring harness, a hard-wired component board, or a printed circuit board, is laborious and time consuming for any network of moderate complexity. In recognition of the drawbacks of such manual testing, there have heretofore been proposed a number of automated testing systems based on a variety of different techniques.
A significant drawback involved in some of the prior art techniques is that redundant checking occurs. In particular, one prior art technique employs seriatim steps such that each network node is individually tested against every other network node. The number of such seriatim steps necessary to check out a network is a factorial function of the number of network nodes. Thus, an enormous number of seriatim steps are involved in testing a network of moderate complexity. For a test of a printed circuit board having, for example, 1000 network nodes, many minutes are required to complete all the seriatim steps even though a very high clock rate is used to control the stepping operation.
Separate and also significant drawbacks are involved in other prior art techniques. In particular, one prior art technique employs simultaneous parallel testing steps. In order to do this it is necessary to provide separate, parallel-operating test units, and this involves considerable complexity and attendant expense. Other prior art techniques employ bulk-shorting methods in conducting the continuity-verification testing. In bulk-shorting, a plurality of the network nodes are externally connected together by virtue of the operation of the testing apparatus. One of the problems that has arisen from using such bulk-shorting relates to the difficulty of locating where a fault lies in a faulty network. To solve the problem created by the bulk-shorting technique involves additional testing time and further complex testing apparatus.